1. Field of the Invention
This invention relates to integrated circuit (IC) fabrication technology, and more particularly, to integrate the shallow trench isolation (STI) process and the storage node process into the fabrication of a dynamic random-access memory (DRAM) device.
2. Description of Related Art
In IC fabrication, the primary goal is to make the resulting IC device as highly integrated as possible. To achieve this goal, the various semiconductor components in the IC device should be sized as small as possible in accordance with the design rules. In the case of DRAM, however, the downsizing of the device would also reduce the size of its data storage capacitor, and hence reduce the capacitance of the capacitor, resulting in a reduced data retaining capability of the capacitor. A DRAM capacitor with a smaller capacitance would require more frequent refreshing of the data stored therein, and thus would be more power consumptive and less reliable to operate.
Presently, in order to enhance the capacitance in the gradually reducing of the substrate area occupied DRAM, many 3-dimensional types of capacitors with complicated structure have been proposed to increase the capacitance of the DRAM capacitor. However, the more complicated the capacitor structure is, the higher the capacitor is. Therefore, the capacitor-over-bit line (COB) layout is often used in the fabrication of the storage node, so that the capacitor is not limited by space.
However, the COB structure makes the height of the memory region higher than the peripheral circuit region. Therefore, the planarization process of the oxide layer covering the capacitor is more complicated. Moreover, the capacitor in the memory cell region is formed after the conducting plug in the peripheral circuit region is formed and the oxide layer on the conducting plug is planarized. Therefore, the contact opening/via opening in the peripheral circuit region have higher aspect ratios, so that the etching of the contact opening/via opening and the deposition of metal are more difficult. Moreover, the subsequent metal line process is more difficults too.